1. Field of the Invention
The present invention is directed to endless belts, including endless V-belts, endless multi-V-ribbed belts and synchronous belts.
2. Description of Related Art
V-belts and multi-V-ribbed belts in particular are conventionally employed for the transmission of peripheral forces in drive systems. Conventional belts comprise a flexible, generally elastomeric main belt body portion defining an undercord- or compression section, an overcord- or tension section and a tensile- or load-carrying section disposed between the undercord and overcord sections. The load-carrying section in turn generally comprises a longitudinally extending highly resilient tensile member typically formed of one or more cords, which is conventionally embedded in or surrounded by an adhesive- or gum rubber composition generally formed from one or more rubber plies or layers.
The frictional engagement between the belt drive surfaces and the drive pulleys or sheaves is generated by the surface of the belt body undercord, with the drive load being borne by the tensile member. The purpose of the adhesive gum is to hold the tensile member in place within the composite belt structure, thus high adhesion and tear strength properties are generally required of these compositions.
In order to provide requisite tear strength properties, it is conventional practice to utilize in forming adhesive gum members a rubber composition characterized by relatively low cross-link density and/or relatively low modulus. Decreasing the cross-link density of a given rubber gum composition generally results in improved tear strength, and also results in a generally proportional decrease in its modulus. A problem exhibited by multi-V-ribbed belts and particularly those operated within high load drives is that of edgecord failure, wherein at least a portion of the tensile cord exposed at the lateral edge of the belt breaks free of the adhesive gum member during operation. This belt failure mode is particularly troublesome since its first sign or indication is frequently catastrophic failure of the belt. From a maintenance perspective, those failure modes exhibiting some early indication of the onset of a potential problem and hence allow for remedial action prior to catastrophic failure, are generally favored over failures as exemplified by edgecord failure.
Increased operational safety- and maintenance requirements of belt drives have led to an increased demand for disturbance-free belts, including V-belts and multi-V-ribbed belts, having a long and predictable service lifespan.
It would be advantageous to provide endless belts, including V-belts and multi-V-ribbed belts and synchronous belts, that exhibit an increased, generally predictable service lifespan, and an improved load-carrying capability compared to belts of the prior art, and particularly such belts which may be suitable for use in high dynamic loading conditions exemplified by contemporary automotive accessory drive applications.
The present invention provides an endless belt comprising a cured rubber composition in contact with at least a portion of a longitudinally-extending tensile member, exhibiting at least one of a complex modulus of at least 15,000 kPa as measured at a temperature of 175xc2x0 C., a strain of 0.09 degrees and a frequency of 2000 cpm; and a tensile modulus at 125xc2x0 C. and 10% elongation of at least 250 pounds per square inch (xe2x80x9cpsi,xe2x80x9d) (1.724 MPa).